AN INTER-ORGANIZATIONAL PEER-TO-PEER WORKFLOW

MANAGEMENT SYSTEM

P2P based Virtual Organization Concept

A. Aldeeb, K. Crockett and M. J. Stanton

Department of Computing and Mathmatics

Manchester Metropolitan University, Manchester, M1 5GD, U.K.

Keywords: Inter-organizational workflow management system, Intra-organizational workflow management system,

Peer-to-Peer, Virtual organization, Exception handling, workflow adaptability, Case-based reasoning.

Abstract: Current inter-organizational cooperation technologies and approaches do not adequately support cross-

organizational workflow. These approaches concentrate on automating the public workflow in isolation

from the internal workflow management systems inside the cooperating organization. Integrating Peer-to-

peer (P2P) and workflow technology enables virtual enterprises to dynamically form and dismantle

partnerships between organizations workflow management systems. In addition, P2P workflow based

systems support various forms of workflow interoperability e. g capacity sharing, chained execution,

subcontracting, case transfer, loosely coupled and public to private approach. This paper describes a novel

peer-to-peer inter-organizational workflow management framework (P2P inter-org WFMS), which includes

workflow advertisement, workflow interconnection, and workflow cooperation. Each organization acts as a

workflow peer (WFP) in a virtual enterprise. Sun Microsystems’s JXTA P2P networking environment is

used for prototype implementation. XPDL (XML Process Definition Languages) is used for process

definition as it offers portability between different Process Design tools. The internal WFMS in each

organization is being implemented using TIBCO Business Studio ™.

1 INTRODUCTION

Workflow is the automation of business processes,

in which tasks, documents and information are

passed from one participant to another for action,

according to a set of procedural rules. A workflow

management system (WFMS) is the software tool

for defining, executing and monitoring the

workflow. Current workflow management systems

focus on the automation of business processes within

the boundaries of a single organization (Liu, et al,

2005). However, as a result of the current increase in

cooperation across organizational boundaries, there

is an increased need for inter-organizational

workflow management systems (inter-org WFMS).

Traditional WFMS are based on the following

requirements (Riempp and Nastansky, 1997): (1) all

actors, routing paths and storage locations in the

workflow are known. (2) Legal, organizational and

security aspects are under control of a single

management. (3) Hardware, operating systems and

workflow management applications are mostly

homogeneous. In contrast, for inter-org WFMS, the

actors, routing, and storage locations are not

established in advance. In addition, the organizations

involved have different legal and organizational

systems, different security aspects, and

heterogeneous hardware, operating systems and

workflow applications.

The cooperation between organizations to

execute a shared process can take the form of a

“virtual organization”. Riempp (1998) defines the

virtual organization (VO) as a temporary coalition of

several, legally independent organizations, with the

purpose of offering a jointly manufactured product

or jointly provided service to customer who perceive

the VO as a singular entity. Virtual organizations

require flexible, on-the-fly alignment of business

partners; in other words, adaptive workflow

capabilities (Buhler and Vidal, 2005).

Recently, researchers have shown an increased

interest in the integration of P2P and workflow

technology to improve efficiency (Berry and

Muhlberger, 2002; Coon, 2002; Yan, 2006; Fakas

Aldeeb A., Crockett K. and J. Stanton M. (2008).

AN INTER-ORGANIZATIONAL PEER-TO-PEER WORKFLOW MANAGEMENT SYSTEM - P2P based Virtual Organization Concept.

In Proceedings of the Tenth International Conference on Enterprise Information Systems - SAIC, pages 85-92

DOI: 10.5220/0001682600850092

 SciTePress

and Karakostas, 2005; Aldeeb et al, 2007). P2P is an

innovative technology that is both flexible and

scalable and provides communication autonomy.

Furthermore, P2P WFMSs are proposed to avoid the

bottleneck and the central point of faults caused by

client/server workflow systems and to improve

scalability, system openness and support

incompletely specified processes. The aim of the

research presented in this paper is to extend the

current P2P WFMSs to an inter-org WFMSs. A

novel peer-to-peer inter-org WFMS framework

which overcomes the limitation of the current inter-

org WFMSs is proposed. This paper is organized as

follows, in section 2, some existing inter-

organizational cooperation technologies and

workflow approaches are presented along with a

discussion of intra-organizational P2P WFMSs. The

proposed inter-organizational P2P WFMS with its

architecture is introduced in section 3. Prototype

implementation is described in section 4, and section

5 concludes the paper with discussion of future

work.

2 RELATED WORK

2.1 Inter-organizational Cooperation

Technologies

Electronic Data Interchange (EDI) is traditionally

used in e-commerce to exchange standardised

structured data between cooperating organizations

(Aalst, 2000a). A Value Added Network (VAN) is

used for EDI transmission for security and additional

features. Despite the benefits of using VAN, it is

complex, has multiple interpretations, and requires

significant technical expertise to deploy. For these

reasons, e-commerce is moving to Web-Based EDI,

which allows organizations to interact with their

partners using the Web. However, EDI solutions are

concentrating on the data transaction and there is no

explicit inter-organizational workflow features (e.g.

allocating and re-allocating task to the participants,

coordination and routing and monitoring).

Integrating EDI technology with workflow is

required for efficient e-commerce.

Web services are now the standard for e-business

and requires several XML-based technologies to

transport and to transform data between programs

and databases (Newcomer, 2002), including WSDL,

SOAP and UDDI. Web services represent loosely

coupled interactions, which are well suited to

integrating disparate software domains and bridging

incompatible technologies. Web services are

simpler than EDI and it is easier to exchange

electronic documents via the internet. Perrin et al.

(2003) implement the middleware between partners

in a VO as web services to provide dynamic and

flexible integration between them. The electronic

business XML (ebXML) is another technology to

enable business-to-business (B2B) transactions by

exchanging a standard XML-based business

messages (Newcomer, 2002). The ebXML

messaging specification is based on SOAP, with

attachments. It does not use WSDL and UDDI but

does add several qualities of service, such as

security, guaranteed messaging mechanism. ebXML

architecture extends basic Web services concepts

and they overlap in many areas. In general, ebXML

specifications can be seen as enhancements to Web

services. These cooperation technologies are tools

for inter-organizational cooperation without explicit

inter-organizational workflow mechanism. Extra

effort is needed to add important workflow aspects,

such as autonomous actions, deliberatively

cooperative behaviour, messages routing to

participants, and querying other participants for

status information of a workflow instance.

2.2 Inter-organizational Workflow

Approaches

Aalst and Weske (2001) proposed a Public-To-

Private approach to inter-organizational workflows

based on a notion of inheritance. This approach

consists of three steps: (1) create a common

understanding of the inter-organizational workflow

by specifying a shared public workflow, (2) partition

the public workflow over the organizations involved,

and (3) for each organization, create a private

workflow which is a subclass of the respective part

of the public workflow.

CrossFlow (Grefen et al, 2001) is an approach

aimed at providing high-level support for workflows

in dynamically formed virtual organizations. In

CrossFlow, partially defined contracts are used by

service providers to advertise their services, and by

service consumers to search for services. As such,

the contract is the basis for dynamic partnerships. A

contract specification language is needed to form the

matchmaking process and to generate the contract

enactment infrastructure dynamically.

The Workflow-based Internet Service (WISE)

(Lazcano, G. et al., 2000) is aimed at designing, and

implementing software tools for business to business

e-commerce over the Internet. The designed

software platform includes four modules: process

definition module, process enactment module,

ICEIS 2008 - International Conference on Enterprise Information Systems

monitoring and analysis module, and coordination

and communication module.

Chebbi et al. (2006) propose a view-based

approach to dynamic inter-organizational workflow

cooperation. This approach allows for partial

visibility of workflows and their resource in the

cooperating organizations. Varying degrees of

visibility of workflows enable organizations to retain

required levels of privacy and security of internal

workflows.

2.3 Intra-organizational P2P Workflow

Management Systems

In P2P WFMS (Fakas and Karakostas, 2005; Yan,

2006; Aldeeb et al, 2007), peers join “virtual

communities” according to their capabilities and

discover each other using the services provided by

an open P2P network. The coordination is

performed by notification messages exchanged

between peers. Two functions are conducted by P2P

WFMS: A Build-time function, which includes

workflow process modelling, storing process

definitions and distributing the process to workflow

peers, and a Run-time function, which includes

workflow instantiation and task coordination. P2P

network provides services that include advertisement

services, group services, peer services, pipe services,

and discovery services. In P2P WFMS, a workflow

peer (WFP) is a software component that can reside

on any machine on the P2P network enabling direct

communication with other workflow peers to enact

the workflow process. The internal structure of the

WFP consists of user, task, and flow components. It

also maintains four data repositories – a peer

repository, a resource and tools repository, a task

repository and a process repository. Each WFP is

associated with a workflow participant and each

performs a part of the workflow. Once the task is

completed, the WFP informs its successor and the

next task of the process is executed. Process co-

ordination is achieved by the exchange of both

information and control messages between peers.

The few proposed P2P WFMS in the literature

are designed for intra-organisational workflow

scenarios (Yan, 2006; Fakas and Karakostas, 2005;

Aldeeb et al, 2007). Despite the advantages of

applying P2P for intra-organisational WFMS, it is

unlikely that all business circumstances in one

organization would require enforcement of a peer to

peer workflow where no one has the overall control.

In other words, P2P intra-organisational workflow is

not a general solution and will be based on the

requirements and the internal structure of the

organization. However, given the discussion of

Inter-organisational WFMS in section 2.2, P2P

WFMS would seem a good general solution for

inter-org WFMS where no central control exist and

the partners are autonomous workflow actors, who

can join and leave VO at any time. In addition, the

participating organizations can implement internal

centralized client/server or decentralized P2P

WFMS based on their requirements.

A novel inter-org WFMS is introduced in the

next section. This system will play the role of

business process integration and management

(BPIM) which involves linking both intra-

organizational and inter-inter-organizational

workflow together to achieve the desired business

process. The inter-organizational system is based on

a P2P platform while the internal WFMSs for the

organizations involved can be decentralized P2P

WFMS or classical centralized client/server WFMS.

3 INTER-ORG P2P WFMS

For inter-organizational business processes, the

execution of workflow may generate a very high

load. This load can affect workflow servers and the

underlying communication network (Bauer et al.,

2003). To improve scalability and efficiency,

integrating P2P technology with inter-organizational

workflow is proposed. In inter-org WFMS, there is

cooperation between information systems that

belong to autonomous organizations; they can at any

time join or leave the shared process. This can be

achieved by applying P2P workflow for inter-

organizational WFMSs where P2P WFMS can be a

promising solution. Each organization involved in

the inter-org workflow will be represented by a

workflow peer (WFP) and these peers will form a

P2P virtual organization. The P2P open network will

be the gateway between the various WFMS of the

cooperating organizations. The goal is to utilize P2P

technology to support organizations involved in a

shared cooperative workflow across organizational

boundaries. A public workflow model is agreed

between different organizations which collaborate as

peers, while keeping their internal private workflow

within their boundaries.

Figure 1 shows an overview of the proposed P2P

inter-organizational workflow management system

using a simple case study. In the case study, three

organizations customer, supplier and manufacturer

are involved in managing a workflow process. This

includes; workflow advertisement, workflow

interconnection, and workflow cooperation. Each

AN INTER-ORGANIZATIONAL PEER-TO-PEER WORKFLOW MANAGEMENT SYSTEM - P2P based Virtual

Organization Concept

organization acts as a workflow peer (WFP) in this

process. The three workflow peers discover each

other by the advertisement service provided by the

P2P network infrastructure. Communication

between peers is achieved using structured

messages. The detailed mechanism and the

functionalities of the peer-to-peer workflow system

can be found in (Yan, 2006; Fakas and Karakostas,

2005; Aldeeb et al, 2007). As shown in Figure 1, the

customer organization is implementing an intra-org

P2P WFMS. When the customer participates in

forming the VO, its inter-org WFP will be part of

two P2P groups. The first group is an internal group

within the boundary of the organization while the

second group is the external VO group. However,

the other two partners in the VO implement a client-

server internal WFMS. Existing workflow

management systems can plug into the P2P VO if

they can fulfil the following two conditions: First,

the WFMS can call an external application (which is

the virtual organization WFP in this case). Second,

the WFMS allows external applications to invoke

any step within its workflow.

Figure 1: Inter-org P2P WFMS overview.

Figure 2 shows the sequence diagram for the inter-

org workflow. This includes three phases of

interactions. The first phase is WFP identification

where associated WFPs for customer, supplier, and

manufacturer publish their services and join

different groups of a specific product or service e.g.

(customers will form a group of customer of specific

product). Each WFP find a desired partner. Second

phase is the WFP interconnection; starting with

electronic negotiation and connection then a virtual

P2P organization is formed. The third phase is WFP

Figure 2: Inter-organizational P2P WFMS interaction

sequence diagram.

cooperation, instantiating a workflow instance and

coordination of tasks by message exchange between

peers. In addition, one of the cooperating workflow

peers in the virtual organization will play the role of

‘Exception Handling Peer (EHP)’. The function of

the EHP is handling the workflow exceptions and

applying an appropriate recovery policy. The

exception handling mechanism is described in

section 3.3.

3.1 Inter-org WFP Internal Structure

Figure 3 shows the high level internal structure of

the WFP. This peer consists of the following parts: a

user interface to create, deploy and monitor the

workflow, an enactment component which serves as

a workflow engine to enact the tasks associated to

this peer, a process repository to store the workflow,

and an exception handling unit. There are two

network interfaces: the first one is to send and

receive messages to and from other peers in the

virtual organization. The second interface to invoke

and exchange information with the internal WFMS.

Manufacturer

P2P Virtual

Organizatio

VO Peer

Intra-org

P2P

WFMS

Internal

WFMS

Internal

WFMS

Supplier Customer

VO Peer

VO Pee

Customer WF

Peer

Supplier WF

Peer

Manufacturer

WF Peer

P2P Advertisement

Service

Publish ()

Partner

Found ()

Partner

found

()

Partner

found ()

Negotiate ()

otiate

()

Connect ()

Connect () Connect ()

Request ()

Response ()

Delivery ()

Workflow

peers

identifica-

tion

Workflow

peers

interconn-

ection

Workflow

peers

cooperat-

ion

otiate

()

ICEIS 2008 - International Conference on Enterprise Information Systems

3.2 Build-time and Run-time Function

of the System

Figure 3: Inter-org WFP Internal Structure.

Loosely coupled is a mechanism to model and

analyse inter-organizational workflow where each

partner takes care of a specified part of the process

(Aalst, 2000b). In this mechanism, the partners are

working independently but synchronization at

certain points is necessary to ensure the correct

execution of the whole process. The proposed

system can be considered as loosely coupled P2P

system. During build-time, the workflow peers in the

virtual organization model and define their parts in

the public workflow and the message structure is

agreed between them. At run-time the workflow

initiator peer is responsible for initiating a workflow

instance. The coordination of this workflow instance

will be achieved by notification messages exchange

between peers.

3.3 Adaptability and Exception

Handling

Workflow adaptability is the ability of the workflow

processes to react to exceptional circumstances

(Sadiq et al., 2005). So far, a little progress has been

reported in addressing exception handling in inter-

organizational business processes (Luo et al., 2003;

Reichert et al., 2003). Workflow exceptions in the

P2P WFMS can be classified to two types of

workflow exceptions: local workflow exception and

global workflow exception. Local workflow

exception affects the task of one workflow peer. The

workflow peer can handle this exception by applying

one of two possible self-recovery policies; forward

recovery or backward recovery. Forward recovery

policy is based on correcting and isolating the effect

of the exception and returning the workflow task to a

normal state so the normal operation can be

continued. In contrast, backward recovery policy is

based on restoring the workflow task to a consistent

state that occurred before the appearance of the

exception. If the local workflow exception can not

be handled within the affected workflow peer, it can

propagate to the other workflow peers leading to a

global workflow exception. This type of exceptions

will, of course, affect more than one workflow peer

and a coordinating node is required to deal with this

exception. In this research, the coordinating node is

the exception handling peer (EHP). The EHP can be

a dedicated peer in the VO or any other workflow

peer with an exception handling capabilities can play

this role in addition to its basic role. The EHP

captures exceptions from the workflow peers,

characterizes the exceptions and applies a recovery

policy. This mechanism is based on separating the

business logic and exception handling logic to make

it easy to keep track of both (Hagen and Alonso,

2000). Furthermore, this will facilitate the process of

verification and later modification of business and

exception handling logic. In addition, the EHP can

select an appropriate exception handler based on the

situation and according to prior knowledge.

In P2P WFMS as a distributed system, backward

recovery of one workflow peer of communicating

peers will often require other peers in the group to

be rolled back because of the interdependencies

caused by message communication. The result is a

cascade of rollbacks called the ‘domino effect’

(Miller and Tripathi, 2004). To avoid the domino

effect in the proposed P2P WFMS a conversation

scheme (Miller and Tripathi, 2004) is used. A P2P

conversation is formed by a group of workflow

peers affected by an exception, and a workflow peer

in the P2P conversation can only communicate with

workflow peers that are in the same conversation.

This can prevent the error propagation and limits the

domino effect. In exception handling mode, the EHP

coordinates the exception handling process in the

P2P conversation. The P2P conversation represents

an atomic action consisting of interactions in a group

of peers. After the effect of the exception is

contained and resolved, the P2P conversation will be

dissolved and the workflow peers will return to the

normal mode of the P2P WFMS.

The EHP is provided with a Case Based

Reasoning (CBR) unit to handle exceptions which

need to be managed in similar way, but may occur in

different instances. CBR (Watson, 1997) is an

artificial intelligent technique which can be defined

as the process of solving problems by using or

Use

Process

Repositor

Associated Inter-org workflow participant

Send/Receive

Message

Enactment

Component

Public to private

Interaction with other

virtual or

anization WF

Exception

Handling

Module

Interaction with internal

WFMS

AN INTER-ORGANIZATIONAL PEER-TO-PEER WORKFLOW MANAGEMENT SYSTEM - P2P based Virtual

Organization Concept

adapting solutions to old similar problems. CBR can

be described by the CBR-cycle which comprises

four activities (Watson, 1999):

1- Retrieve similar cases to the problem

description

2- Reuse a solution suggested by a similar

case

3- Revise or adapt that solution to better fit

the new problem if required

4- Retain the new solution once it has been

confirmed or validated

CBR can add great value to the exception

handling in workflows as the CBR system collects

and stores cases; the WFMS becomes more resistant

because it has a large set of knowledge to handle

future exceptions (Cardoso et al., 2001). The nearest

neighbour technique is a widely used in CBR

(Hwang and Tang, 2004). The similarity between the

new exception (target) and previously stored

exceptions (source) is determined using the

following equation:

(1)

Where T is the target exception case; S is the

source exception case; i an individual exception

attribute from 1 to n; f a similarity function for

exception attribute i in exception cases T and S; and

w the importance weighting of exception attribute i.

In the VO, exception attributes, which are stored

as a case include: workflow instance number, status

of workflow instance, exception type, exception

description, time of creation, use counts, associated

workflow peer number, exception solution. The

nearest neighbour approach is applied by first

retrieving similar exceptions and then selecting the

nearest similar exception. The associated exception

handler is then applied. If the distance between cases

is greater than a set similarity threshold then a new

temporary case is established and a new exception

handler is created. Frequent appearance of certain

exceptions and the usage of their associated stored

cases may lead to creation of a new version of the

workflow schema and business process evolution.

4 PROTOTYPE

IMPLEMENTATION

Currently, the feasibility of the ideas presented in

this paper are being implemented, validated, and

tested using a proof-of-concept prototype. Current

progress on the prototype and a case study are

described in this section.

4.1 Workflow Specification Language

and Implementation Tools

Sun MicroSystem’s JXTA is the networking

environment for P2P while XPDL (XML Process

Definition Languages) is used for process definition

as it offers portability between different Process

Design tools. The internal WFMS in each

organization is being implemented using TIBCO

Business Studio™. TIBCO Business Studio™ is

selected because it supports several industry

standards, namely Business Process Modeling

Notation (BPMN) and XPDL. In addition, TIBCO

Business Studio™ provides two types of tasks; send

task and receive task. Send Tasks are used to send

messages to a system or person outside of the

Process (in this prototype send task is used to call

and instantiate the JXTA platform for the VO

workflow peer). Receive Tasks are used to wait for a

message from a system or person outside of the

Process (in this prototype receive task is used by the

VO workflow peer to invoke the internal WFMS).

4.2 Case Study

Figure 4 shows the case study used for the prototype

implementation in Petri-net representation. Three

organizations, namely a customer, a supplier and a

manufacturer, are involved in managing a workflow

process. A workflow instance starts at the customer

internal WFMS when a specific product is required.

The internal WFMS will send an external request for

this product to the workflow peer which represents

the customer in the VO. This request is an XML

message contains the order details (Order No,

product Name, Description and Quantity etc). The

customer workflow peer will initiate a public

workflow instance by sending the order to a selected

supplier workflow peer which in turn will select a

manufacturer workflow peer. A P2P VO is formed

to manage a public workflow instance (product

order). The status of this public workflow instance at

any time is available for all the VO peers because

every VO workflow peer is capable to query other

workflow peers for status information of workflow

instance. The sequence of these tasks and interaction

is shown in figure 4. Another scenario for the

prototype implementation will consider that the

customer has an internal P2P WFMS. In this case,

=),( STSimilarity

wSTf ×

∑

),(

ICEIS 2008 - International Conference on Enterprise Information Systems

Figure 4: The prototype implementation and public-to-private workflow interaction.

JXTA P2P network is the infrastructure for both

customer internal P2P WFMS and The P2P VO. A

workflow peer in the internal customer WFMS will

be part of the VO peers as well. This workflow peer

will initiate a workflow instance for a specific

product and the order will be sent to the supplier

peer and manufacturer peer. The rest of the

workflow process is similar to the first scenario. In

this case study, the customer workflow peer in the

VO is provided with an exception handling

capabilities and will play the role of the EHP in

addition to its basic role. Ad-hoc changes will be

made in the running workflow instance to examine

the exception handling procedures mentioned in

section 3.3.

5 CONCLUSIONS AND FUTURE

WORK

Applying P2P technology for inter-organizational

workflow is the novelty of the ideas presented in this

paper. Inter-organizational P2P WFMS can be

considered as a business process integration and

management (BPIM) tool which facilitates linking

both intra-organizational and inter-inter-

organizational workflow together to conduct the

desired business process. In addition, P2P workflow

management systems can be a promising solution for

inter-organizational workflow because of the

autonomy that facilitates the partners which act as a

workflow peers in inter-organizational business

process. A P2P inter-organizational workflow

approach provides the mechanism for workflow

peers to do the following: discover other peers and

their services, publish their available services,

exchange data and control messages with other

peers, route messages to other peers , query peers for

status information related to a workflow instance,

and dynamically form and dismantle groups. The

P2P WFMS previously designed for intra-

organizational WFMS is being upgraded for inter-

organizational scenario using a prototype

implementation for a case study. The adaptability

and exception handling can be achieved by applying

workflow peer self-recovery policies, P2P

conversation, and the EHP concepts. The EHP

within the virtual organization will be responsible

for handling the exceptions in the P2P conversation.

This peer will acquire knowledge from previous

exceptions using case based reasoning. Evaluation of

the proposed system will be carried out and

comparison with other inter-org workflow

approaches.

Receive

Order

from

Internal

WFMS

Select

lie

Send Order

Receive

Invoice

Make

Receive

Delivery

Date

otify

Internal

WFMS

Receive

Orde

Select

Manufacture

Send Order to

Manufacture

Send

Invoice

Receive

Confirm

Deliver

Customer WF Peer Supplier WF Peer

Produce

der

Deliver

Orde

Manufacturer WF Peer

Customer Internal

WFMS

End

Start

External Task

eques

External Task

Res

onse

P2P Virtual Organization (VO) Intra-org WFMS

AN INTER-ORGANIZATIONAL PEER-TO-PEER WORKFLOW MANAGEMENT SYSTEM - P2P based Virtual

Organization Concept

Future work will include exception classification

in P2P inter-organizational workflow and calculation

of exception’s re-occurrence rate in the VO. This

will help to confirm the value of using CBR as a

methodology for exception handling in the system.

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